A recurrent clinical hallmark of heart failure (HF) is the occurrence of arrhythmias, which contribute to the increased incidence of sudden cardiac death in HF patients and can in turn also lead to worsening HF. Despite the clear link between HF and arrhythmia, no applicable treatment has been identified specifically targeting these electrical abnormalities. The PI and his mentors have recently discovered that cardiac myosin binding protein c (cMyBP-C) phosphorylation might play a role in modulating calcium (Ca2+) handling in the heart. This can have profound implications in understanding the mechanism leading to arrhythmia during HF and might identify novel therapeutic strategies. Indeed, cMyBP-C phosphorylation is extensively phosphorylated in the healthy heart and severely depleted in HF, pathological hypertrophy, ischemic injury and atrial fibrillation. The planned investigation will exploit well established methods of assessing cardiac function in vivo, as well as develop and refine novel tools to further extend the in vivo findings into single isolated cardiac ventricuar myocytes. Work by the PI and his mentors has established several transgenic animal models that will be critical to study how cMyBP-C can lead to arrhythmogenesis, and show that mice harboring mutations preventing phosphorylation of cMyBP-C display severe arrhythmia and cardiac death following adrenergic stress. We hypothesize that cMyBP-C phosphorylation is necessary for proper Ca2+ handling in the myocardium. Therefore, the overall objectives of this proposal are to: 1) determine the propensity for arrhythmias in mice harboring mutations ablating (AllP-) or mimicking (AllP+) phosphorylation of cMyBP-C, 2) investigate the molecular causes of altered Ca2+ in isolated cardiomyocytes. The unique feature of the proposed work is the combination of in depth in vivo study and single cell experiments in a richly interactive environment with a strong record of success in such work. For the PI, the investigation nicely supports his long-term plan of conducting interdisciplinary research related to cardiac function, with the prospect of broadening our understanding of the pathogenesis of heart failure.